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Subsurface Mining

Subsurface Mining

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Subsurface Mining

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  1. Subsurface Mining

  2. What are mineral resources? • Concentrations of naturally occurring solid, liquid, or gaseous material in or on the earth’s crust in a form and amount such that extracting and converting it into useful materials or items is currently or potentially profitable. There are Metallic (ex. Iron and Tin ores) or non-metallic (ex. Fossil Fuels, Sand and Salt). There are also energy resources

  3. Ores • Ores are rocks containing enough of one or more metallic minerals to be mined profitably • Ores are formed from Magma when magma flows up into the earth’s crust at divergent and convergant plates. As it cool, it crystallizes into various layers of mineral containing igneous rocks

  4. Ores ctd. • As sediments settle they can form ore deposits by sedimentary sorting and precipitation • Manganese Nodules are about 30-40% manganese with small amounts of other metals • Manganese Nodules are a source of metals on ocean floor

  5. Ore Grade • -The concentration of an element of interest in a potentially mineable ore deposit.

  6. Hydrothermal process • Two tectonic plates retreat from one another, magma begins upwelling into earths crust as well as seawater • The seawater becomes superheated and dissolves metals from rock or magma • Dissolves minerals cool and form Hydrothermal ore deposits

  7. How minerals are found Using aerial photos and satellite images to reveal protruding rock formations associated with certain minerals. Radiation measuring equipment-Uranium Magnetometer-Iron Gravimeter Seismic Surveys-explosives

  8. Where Are These Minerals? • Identified resources: deposits of a nonrenewable mineral resource with a known location and quantity, and whose existence is based on evidence • Undiscovered resources: potential supplies of a nonrenewable mineral resource based on theory but in unknown amounts and unknown locations • Reserves: identified resources where nonrenewable minerals can be extracted currently

  9. How are these minerals extracted? • Surface Mining: Equipment strips away the overburden of soil and discards it as waste called “spoils” • Open-pit Mining: machines dig holes and remove ores • Dredging: chain buckets and draglines scrape up underwater mineral deposits

  10. More Extracting • Area Strip Mining: when terrain is fairly flat the overburden is stripped and a power shovel cuts out the mineral. Then the hole is refilled and another one is cut next to it. If the land is not restored, it leaves a series of rubble hills called spoil banks • Contour Strip Mining: used on hilly terrain, and a power shovel cuts into the side of a hill. If land is not restored, it leaves a bank of soil called a highwall • Mountaintop Removal: uses explosives and large machinery to remove the top of a mountain to get at the minerals inside it. Causes considerable environmental damages

  11. Environmental Impacts of Mining

  12. Scarring and disruption of land • The Department of the Interior estimates that about 500,000 mines dot the U.S. landscape, mostly in the West. Clean-up costs are estimated in the tens of billions of dollars. Collapse or subsidence of land above underground mines • Houses to tilt • Sewer lines to crack • Gas mains to break • Ground water systems to be disrupted

  13. Erosion of toxic-laced mining wastes • The EPA estimates that mining has polluted 40% of Western watersheds. Acid Mine Drainage • When rainwater seeping through a mine or mine wastes: • Carries sulfuric acid to nearby streams • Contaminates water supplies • Destroys aquatic life

  14. Air pollution • Emission oof toxic chemicals into the atmosphere • In the U.S., the mining industry produces more toxic emissions than any other industry • The most air pollution comes from smelting which is the process of separating the metal ore from the gangue. Mining severely alters the natural environment, thus harming all wildlife in the vicinity.

  15. Economic Depletion and Depletion Time • Economic Depletion- Exhaustion of 80% of the estimated supply of a nonrenewable resource. • Depletion time-The time it takes to use up a certain proportion (usually 80%) of the reserves of a mineral at a given rate of use.

  16. Reserve-to-Production-Ratio • -A traditional measure of the projected availability of non-renewable resources. It is the number of years that proven reserves of a particular nonrenewable mineral will last at current annual production rates.

  17. Surface Mining Control & Reclamation Act 1977 • -Requires mining companies to restore most surface-mined land so it can be used for the same purpose as it was before it was mined. • -Levied a tax on mining companies to restore land that was disturbed by surface mining before the law was passed.

  18. General Mining Law 1872 • -Under this law, a person or corporation can assume legal ownership of parcels of land on essentially all U.S. public land except parks and wilderness areas by patenting it. This involves (1) declaring the belief that the land contains valuable hard rock minerals, (2) spending $500 to improve the land for mineral development, (3) filling a claim, (4) paying an annual fee of $100 for each 8 hectares to maintain the claim whether or not a mine is in operation, and, if desired, (5) paying the federal government $6-12 per hectare for the land. Once purchased, the land can be used, leased, or sold for essentially any purpose. • -Allows mining interests to pay no royalties to taxpayers for hard-rock minerals they remove and not be responsible for any environmental damage they cause.